为什么在将json映射到Java bean期间，Spring MVC为什么将参数[“”]转换为[null]？

Question

I want to know why spring mvc transform [""] to [null] when I use PostMan to test my API. here is my controller:

    @RequestMapping(value = "", method = RequestMethod.POST, consumes = "application/json", produces = "application/json")
public @ResponseBody ResponseEntity<Object> participateRstActivities(
        HttpServletRequest request, @RequestBody RstActivityFrom rstForm)
        throws ServiceException {
          log.info("list size:{}, frist object:{}",rstForm.getRestaurant_ids().size(), rstForm.getRestaurant_ids().get(0));
        }

here is my java bean:

public class RstActivityFrom {

    private List<Integer> restaurant_ids;
    private int activity_id;
    // omit getter & setter
}

here is my request body when I use postman to test my api:

{
 "restaurant_ids":[""],
 "activity_id":119129
}

and the log in controller print : list size:1, frist object:null.

this problem makes me feel confuse, I want to know why. Thanks

Answer 1

Since restaurant_ids is a List and not String, Change your JSON for restaurant_ids:

{
 "restaurant_ids":[],
 "activity_id":119129
}

If you don't want to allow an empty String value for objects mapped from your JSON, you can look into setting the Jackson's ObjectMapper Features as described here:

https://docs.spring.io/spring-boot/docs/current/reference/html/howto-spring-mvc.html

The Java API for Jackson's DeserializationConfig.Feature(s) can be found here:

http://fasterxml.github.io/jackson-core/javadoc/1.9/org/codehaus/jackson/map/DeserializationConfig.Feature.html